This session walks through tons of examples in live coding. You will learn everything you need to know about lambdas and functional programming in Java 8. I’m the supplier. You’re the consumer (and you will get the joke after the session).

1. © Henri Tremblay 2015
Henri Tremblay
Senior Software Engineer
Terracotta, a Software AG company
Learn Java 8: Lambdas and Functional
Programming
@henri_tremblay

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Henri Tremblay

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Henri Tremblay

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Henri Tremblay
• More or less made possible class mocking and proxying
• Coined the term “partial mocking”

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Henri Tremblay
• More or less made possible class mocking and proxying
• Coined the term “partial mocking”

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Java < 8

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Live Coding

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Questions

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Java 5
(2004)

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JAVA 5 GAVE THE GENERIC
TYPES TO THE WORLD
(and also annotations, concurrent collections, enum types, for
each, static imports and so on and so on)

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Type witness
Having
<T> T anyObject()
you can force the type with
MyClass.<List<String>> anyObject()
because
(List<String>) MyClass.anyObject()
gives a warning

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Java 6
(2006, last from Sun)

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JAVA 6 BROUGHT... PRETTY
MUCH NOTHING
(a bunch of performance improvements under the hood, better xml
parsing and the first scripting api)

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Java 7
(2011, first from Oracle)

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JAVA 7 BROUGHT A LOT OF
SYNTACTIC SUGAR
(plus invokeDynamic, ForkJoin, better file IO)

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Switch for strings
switch(s) {
case "hello":
return "world";
case "bonjour":
return "le monde";
}

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Diamond operator
List<String> list = new ArrayList<>();

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Binary integer literals and underscores
int i = 0b1110001111;
int i = 1_000_000;

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Multiple catches
try {
// ... do stuff
}
catch (IOException | SerializationException e) {
log.error("My error", e);
}
Instead of
try {
// ... do stuff
} catch (IOException e) {
log.error("My error", e);
} catch (SerializationException e) {
log.error("My error", e);
}

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Auto Closeable
Before
InputStream in = new FileInputStream("allo.txt");
try {
// … do stuff
} finally {
try { in.close(); } catch(IOException e) {}
}
After
try(InputStream in = new FileInputStream("allo.txt")) {
// … do stuff
}

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File IO API
List<String> lines =
Files.readAllLines(
Paths.get("path", "to", "my", "file.txt"));
// also: file watcher, symbolic links, file locks,
// copy… Look in java.nio.file

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Java 8
(2014)

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JAVA 8: LAMBDA!
(and also a new date API, default methods, metaspace, Nashorn,
JavaFX and CompletableFuture)

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Date / Time API
Core ideas:
Immutable
A time is a time, a date is a date. Not always both (like java.util.Date)
Not everyone uses the same calendar (the same Chronology)
LocalDate, LocalTime, LocalDateTime  Local. No time zone
OffsetDateTime, OffsetTime  Time with an offset from
Greenwich
ZonedDateTime  LocalDateTime with a time zone
Duration, Period  Time span
Instant  Timestamp
Formatting  Easy and thread-safe formatting

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Date / Time API (example)
LocalDateTime now = LocalDateTime.now();
String thatSpecialDay = now
.withDayOfMonth(1)
.atZone(ZoneId.of("Europe/Paris"))
.plus(Duration.ofDays(5))
.format(DateTimeFormatter.ISO_ZONED_DATE_TIME);
System.out.println(thatSpecialDay);
Output
2016-09-06T17:45:22.488+01:00[Europe/Paris]

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Lambda: 11th letter of the Greek alphabet

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(also written as λ-calculus) is a formal system in
mathematical logic for expressing computation based
on function abstraction and application using variable
binding and substitution. It is a universal model of
computation that can be used to simulate any single-
taped Turing machine and was first introduced by
mathematician Alonzo Church in the 1930s as part of
an investigation into the foundations of mathematics.
Lambda calculus

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This is a function:
This is a lambda:
Lambda calculus

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c = sqrt(add(pow(a, 2), pow(b, 2)))
Functional programming

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The End

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Who has learned
something today?
?

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Brian Goetz – State of the lambda
http://cr.openjdk.java.net/~briangoetz/lambda/lambda-state-
final.html
http://cr.openjdk.java.net/~briangoetz/lambda/lambda-
translation.html
Ninja Squad – Lambda Kata
https://github.com/Ninja-Squad/ninjackaton-lambda
Maurice Naftalin’s lambda facts and books
http://www.lambdafaq.org/
Mastering Lamdbas: Java Programming in a Multicore World
Links

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Questions? http://montreal-jug.org
?
http://easymock.org
http://objenesis.org
http:/ehcache.org
Henri Tremblay
http://blog.tremblay.pro
@henri_tremblay